The present invention relates to a cooling apparatus for a water-cooled type outboard motor.
An engine unit of an outboard motor is mounted vertically in such a manner that a crank shaft of the engine unit is disposed vertically in a mounted state. The engine unit is formed by assembling a crank case, a cylinder block and a cylinder head. Moreover, an exhaust manifold for gathering flows of exhaust gases discharged from respective cylinders to cause the exhaust gas to flow downwards is provided on one of the side surfaces of the cylinder block.
The engine unit of the structure mentioned above is provided with a cooling apparatus structured to supply sea water, river water or lake water pumped up by a water pump to a water jacket provided for the inside portions of the cylinder block, the cylinder head and the exhaust manifold, respectively.
The conventional cooling apparatus for an outboard motor has a structure that water jackets respectively provided for the cylinder block, the cylinder head and the exhaust manifold are allowed to communicate with one another to cause cooling water to flow in these elements. The water jacket of the cylinder block or the cylinder head is provided with a thermostat to adjust the flow of cooling water to be an adequate quantity to be adaptable to the water temperature to prevent the cylinder from being excessively cooled.
The thermostat is disposed above the uppermost portion of the water jacket. The reason for this arrangement is to obviate a problem which may arise in that air is accumulated in a portion upstream from the thermostat after the thermostat has been opened if the thermostat is disposed lower than the uppermost portion of the water jacket to thereby prevent sufficient circulation of the cooling water around the uppermost cylinder. In this case, the water-cooled engine cannot satisfactorily be cooled down.
Moreover, the cylinder block is provided with a cylinder-surface-temperature sensor for detecting the temperature of the wall of the cylinder and a pressure valve for controlling an oil pressure of the cooling water. In a conventional arrangement, a sensor for detecting a temperature of the cylinder surface and the pressure valve are disposed apart from the thermostat.
However, the conventional cooling apparatus for an outboard motor, having the structure that the cooling water is communicated among the water jackets for the cylinder head, the cylinder block and the exhaust manifold, suffers from deterioration in the efficiency for cooling the portion around the cylinder because of introduction of hot cooling water into the water jackets for the cylinder block and the cylinder head. Moreover, the temperature of the cooling water cannot satisfactorily be controlled by the thermostat.
Since the thermostat of the conventional cooling apparatus for an outboard motor is disposed above the uppermost portion of the water jacket, the thermostat excessively projects over the surface of the engine unit, which results in an enlargement of the size of the engine unit.
Since the cylinder-surface-temperature sensor is disposed apart from the thermostat, the temperatures detected by the cylinder-surface-temperature sensor are not stable. In particular, the temperature of the cooling water cannot easily be controlled during a warming-up operation, thus causing a problem to arise in that an excessively long time is required to warm up the engine unit. In case a breakdown of the thermostat may occur, the cylinder-surface-temperature sensor cannot detect the breakdown.
The structure, in which the pressure valve is disposed apart from the thermostat, cause pipes extending from the thermostat and the pressure valve to be disposed apart from one another. As a result, the structure of a water drainage passage becomes too complicated. Thus, the engine unit cannot easily be assembled and the maintenance of the same cannot smoothly be performed.